The present invention relates to a sheet feeding apparatus and particularly to a sheet feeding apparatus adapted for feeding and placing a front cover received from a transfer path over a specific number of sheets (for example, bound as a booklet) or stacks of sheets supplied from a printing machine or a sorter.
FIG. 13 is a side view showing a schematic arrangement of a conventional sheet feeder for a bookbinding machine. In FIG. 13, a side panel of the sheet feeding apparatus is removed for ease of the description.
As shown in FIG. 13, the sheet feeding apparatus 1 comprises a sheet reception inlet 2a for receiving sheets of paper, a tray 4 for storage of a stack of front covers P, a sheet stack-feed station S for stacking up the sheets and placing a front cover P on a stack of the sheets, a first conveying path 2 extending from the sheet reception inlet 2a to the sheet stack-feed station S, and a sheet conveying mechanism for conveying in a sequence the sheets received at the sheet reception inlet 2a to the sheet stack-feed station S along the first conveying path 2. The sheet conveying mechanism consists mainly of a conveyor belt 2b, transfer rollers 2c to 2g, and a discharge roller 2h. 
The sheet feeding apparatus 1 also includes a second conveying path 8 extending from the tray 4 to the first conveying path 2 for joining with the first conveying path 2 and a sheet feeding mechanism for conveying the front cover P along the second conveying path 8 up to the first conveying path 2. The sheet feeding mechanism comprises a feed roller 5, a transfer roller 6, a drive motor 7, and a pair of feed rollers 8a and 8b. 
The sheet feeding apparatus 1 further includes a sheet transfer mechanism for transferring the front cover P from the tray 4 to the sheet feeding mechanism. The sheet transfer mechanism comprises a pneumatic pump 14 and a drive motor 13 for driving the pneumatic pump 14. A first pulley 13a is mounted on the output shaft of the drive motor 13 while a second pulley 14a is mounted on the rotary shaft of the pneumatic pump 14. A belt 13b is mounted between the first pulley 13a and the second pulley 14a for transmitting the power of the drive motor 13 to the pneumatic pump 14.
The sheet transfer mechanism also includes a blow outlet 18 provided in the tray 4 for communicating via a first conduit 17 to the air outlet of the pneumatic pump 14 to blow up the front cover P in the tray 4, a sucker 10 communicated via a second conduit 11 to the air inlet of the pneumatic pump 14 and arranged for movement between the first position for sucking the front cover P blown up and the second position for transferring the front cover P to the sheet feeding mechanism, a sucker driving mechanism 10a for moving the sucker 10 between the first position and the second position, and a couple of first and second air valves, 12 and 16, for controlling the air intake and the air discharge of the pneumatic pump 14, respectively.
As the pneumatic pump 14 is actuated, a flow of air runs along the first conduit 17 in a direction denoted by the arrow Bb and exits at the blow outlet 18. This action effects an upper region of the stack of the front covers P in the tray 4 and more specifically, lifts up the uppermost front cover P. Simultaneously, a flow of air runs along the second conduit 11 in a direction denoted by the arrow Ba. This action causes the sucker 10 to suck up at its first position the uppermost front cover P lifted up. The sucker 10 is then moved to its second position for transferring the uppermost front cover P to the sheet feeder mechanism. The front cover P received by the sheet feeder mechanism is passed through the feed roller 5 and the transfer roller 6 and between the two feed rollers 8a and 8b as conveyed along the second conveying path 8 to the first conveying path 2.
The transfer of the front cover P to the sheet feeding mechanism by the sucker 10 is continuously carried out as synchronized with the conveying of the sheets along the first conveying path 2. Particularly in case that the sheet feeding apparatus is linked with an advanced digital printing machine, a given number of sheets for one book volume may be received in the order of page at the sheet reception inlet 2a of the first conveying path 2, conveyed along the first conveying path 2, and stacked up in the sheet stack-feed station S. During the conveying of the sheets, the pneumatic pump 14 remains actuated for releasing a blow of air from the blow outlet 18 to lift up the uppermost one of front covers. Before the transfer of the succeeding front cover is initiated, the first air valve 12 remains closed to allow the sucker 10 to suck up no front cover.
In the conventional sheet feeding apparatus, the transfer of a front cover from the second conveying path 8 to the first conveying path 2, and thus to the sheet feeding mechanism, is continuously carried out as synchronized with the timing of conveying the sheets along the first conveying path 2. If a feeding error of the front cover (no transfer of a front cover from the second conveying path 8 or transfer of multiple front covers at one time) occurs in a lot, the reaction is that the movement of the first conveying path 2 is halted and the error is eliminated by adding a front cover to, or removing the excessive front covers from, the lot. This will thus decline the operational efficiency of the apparatus.
Also, as the pneumatic pump 14 is continuously driven to blow a jet of air against the upper ones of the stacked front covers P in the tray 4, its temperature may increase and so the temperature of the jet of air. Accordingly, the front covers P are exposed to the hot air and may deform or curl up at their edges, hence lowering the quality and making their handling difficult at the succeeding step.
The pneumatic pump 14 remains actuated while no transfer of the front covers P is performed. This will increase the power consumption and thus the overall production cost while shortening the life of the pneumatic pump 14. Moreover, the pneumatic pump 14 constantly emits running noises and may cause environmental disruption.
It is thus an object of the present invention to provide a sheet feeding apparatus capable of, if a feeding error of a front cover occurs, readily eliminating the cause of error without halting the main operation.
It is another object of the present invention to provide a sheet feeding apparatus which can improve the environmental conditions of a pneumatic pump.
For achievement of the object of the present invention, a sheet feeding apparatus is provided comprising: a sheet reception inlet for receiving a set of first sheets; a tray for storing a stack of second sheets; a sheet set discharge outlet for releasing out a set of the sheets where the second sheet is placed over the first sheets; a first conveying path extending from the sheet reception inlet to the sheet set discharge outlet; a sheet conveying means for conveying the first sheets received at the sheet reception inlet in a sequence along the first conveying path to the sheet set discharge outlet; a second conveying path extending from the tray to the first conveying path and communicated at a junction with the first conveying path; a sheet feeding means for conveying the second sheet along the second conveying path to the junction with the first conveying path and placing the second sheet over the first sheets; a sheet transferring means for transferring each second sheet from the tray to the sheet feeding means; and a controlling means for controlling the action of the sheet conveying means, the sheet feeding means, and the sheet transferring means, wherein the sheet feeding means is changed to its standby mode when the second sheet is transferred from the sheet transferring means to the sheet feeding means and, upon the first sheets arriving at the junction, starts the sheet feeding operation, thereby the second sheet is conveyed out from the second conveying path and placed over the first sheets.
Also, for achievement of the object of the present invention, a sheet feeding apparatus is provided comprising: a sheet reception inlet for receiving a set of first sheets; a tray for storing a stack of second sheets; a sheet stack-feed station for receiving the first sheets in a stack and placing the second sheet over the stack of the first sheets; a first conveying path extending from the sheet reception inlet to the sheet stack-feed station; a sheet conveying means for conveying the first sheets received at the sheet reception inlet in a sequence along the first conveying path to the sheet stack-feed station; a second conveying path extending from the tray to the first conveying path and communicated at a junction with the first conveying path; a sheet feeding means for conveying the second sheet along the second conveying path and feeding it to the first conveying path; a sheet transferring means for transferring each second sheet from the tray to the sheet feeding means; and a controlling means for controlling the action of the sheet conveying means, the sheet feeding means, and the sheet transferring means, wherein the sheet feeding means is changed to its standby mode when the second sheet is transferred from the sheet transferring means to the sheet feeding means and, upon the first sheets having been stacked in the sheet stack-feed station, starts sheet feeding operation, thereby the second sheet is conveyed out from the first conveying path and placed over the stack of the first sheets.
According to any of the above first and second arrangements, the second sheets are held at the standby mode but not conveyed continuously in synchronization with the conveying of the first sheets such as in the prior art. Accordingly in case that an error occurs during the conveying of the current second sheet, it is readily detected and the succeeding second sheet is held in the standby mode. This allows the error during the conveying of the second sheet to be eliminated without canceling the conveying of the first sheets, hence improving the operational efficiency of the system.
The second embodiment of the present invention may preferably be modified in which the sheet transferring means comprises: a pneumatic pump having an air outlet and an air inlet; a blow outlet provided in the tray and communicated by a first conduit to the air outlet of the pneumatic pump for lifting up each second sheet stored in the tray; a suction means communicated by a second conduit to the air inlet of the pneumatic pump and arranged to move between the first position for sucking the second sheet lifted up and the second position for transferring the second sheet to the sheet feeding means; a suction means actuating means for driving the suction means to move between the first position and the second position; and air valves provided between the air outlet of the pneumatic pump and the first conduit and between the air inlet of the pneumatic pump and the second conduit for controlling the air output and input of the pneumatic pump, wherein while the sheet feeding means is in its standby mode, the air valves are controlled by the controlling means to cancel the air output and input respectively of the pneumatic pump. Accordingly, the time of blowing a jet of air to lift up each second sheet is minimized. This allows the second sheet to be prevented from being injured and degraded in the quality and to be handled without difficulty in the succeeding step.
More preferably, it may be arranged in that while the sheet feeding means is in its standby mode, the air valves are turned off by the controlling means to cancel the air output or input respectively of the pneumatic pump. The pneumatic pump is operated for a minimum duration for transferring the second sheet and remains inactivated in the remaining duration. Accordingly, the operating period of the pneumatic pump can be reduced hence decreasing the power consumption and the running noise. Hence, the pneumatic pump will be extended in the operational life and improved in the environmental conditions. Also, as the pneumatic pump is operated intermittently, its temperature increase can be avoided as cooled down in the inactivated duration. Accordingly, the second sheet will be prevented from being assaulted by a jet of hot air. As the second sheet is successfully prevented from its degradation, it can be handled without difficulty in the succeeding step.
As a preferred embodiment of the present invention, the sheet feeding apparatus may further comprise: sheet detection sensors provided at the entrance of the second conveying path; a discharge tray provided as branched out from an intermediate region of the second conveying path; and a switching gate provided at the branch point to the discharge tray of the second conveying path, wherein the action of the switching gate is controlled by the controlling means so that, in a normal mode, the second sheet is duly conveyed along the second conveying path and, when the sheet sensors detect that two or more of the second sheets are received by the sheet feeding means, the two or more second sheets are discharged to the discharge tray. Accordingly, in case that two or more second sheets are received by the sheet feed mechanism, they are automatically detected by the sheet detection sensors and thus discharged to the discharge tray. Undesired placement of two or more second sheets over a given set of the first sheets can favorably be avoided.